In recent years, model changes frequently take place for producing various types in small lots at manufacturing sites. In order to automate screw tightening work, fitting work or attaching work of components, inserting work of flexible substrates or the like, or polishing work by robots at recent manufacturing sites where the cell production is actively adopted, it is necessary to flexibly address a great variety of components or work procedures. Since the position or orientation in assembly work changes every time a change is made in the component and so a change is made in the order of performing the work, such changes must be addressed. Further, the work of handling flexible objects such as inserting work of flexible substrates is troublesome, and hence is still human-intensive. When the flexible object is brought into contact with a target object and is deflected thereby, a reaction occurs and the human estimates the deflection degree or the position of a flexible object by the reaction received at his/her hand. In this manner, the human can carry out complicated work.
To the contrary, it is very difficult for a robot to perform complicated work in accordance with the obtained reaction, because the force information or positional information of the flexible object which flexure manner or place varies for each trial and cannot be formulated. There is great demand for solving the aforementioned issue and automating such human-intensive works so as to be performed by robots.
Accordingly, what is conventionally employed is a method of teaching works to robots using a teaching pendant or programming. However, teaching through such a method greatly increases the teaching steps. Further, it may be impossible to teach works which require complicated motion such as moving a plurality of joints of a robot at the same time.
As described above, the method of teaching through use of a teaching pendant or programming has limitation.
Therefore, conventionally, what is employed is a method of simply teaching through direct teaching, in which a robot is taught by being touched. The direct teaching is advantageous in that: an intuitive manipulation is possible; and the user can feel the physical reaction occurred by the robot being brought into contact with the target object, whereby the worker can perform a manipulation in accordance with the reaction. On the other hand, it has combined disadvantageous in that: the user cannot support the robot when the robot itself is heavy, and hence cannot manipulate the robot; the user cannot feel the physical reaction occurred by the robot being brought into contact with the target object because the robot itself is heavy; and the robot is dangerous when the robot becomes out of control because the user is touching the robot. Thus, in teaching the robot of poor operability, it is highly important to improve the operability of the robot. Similarly, it is important to secure safety when the user touches the robot.
In connection with the direct teaching, a structure in which a second robot arm is attached by a spring to the arm end leading end part of the first robot arm is considered. Employing the structure having the two robot arms, more precise direct teaching is realized as compared to the conventional structure having only one robot arm (see Patent Literature 1).
Further, a method is used which includes: limiting the motion of the retaining member in the horizontal direction; detecting external environment (a displacement amount or force information of the retained target object); and exerting impedance control. Thus, even in the case where a relatively heavy target object is held, the retaining member can be displaced with a small force (see Patent Literature 2).
On the other hand, in connection with the conveying work of products or the fitting work of heavy components, in the case where the work cannot be achieved by a robot through the method using a teaching pendant or programming because of complexity, the work is performed by two workers. There is strong demand for reducing the burden of the workers using a robot in performing such work. In automating such work, the worker cannot teach the robot through the direct teaching because the product weighs heavy. Accordingly, what is employed is the cooperative conveyance method, in which a robot conveys the gripped heavy product in cooperation with the worker.
In connection with the cooperative conveyance, it is considered to produce an assist force at the robot so that the cooperative conveyance is achieved with a small manipulatory force. The assist force value is obtained as follows. That is, the joint angle of the robot, the arm end position, and the force that the worker cooperatively working with the robot applies to the target object are detected. Based on these values, the viscosity coefficient of the worker's fingertip, the elastic coefficient, and the natural length position of the worker's fingertip are estimated, and the assist force value is obtained based on these values (see Patent Literature 3).